LED display screens are widely used in various fields such as industry, transportation, commercial advertising, and information publication due to their advantages such as high gray scales, large viewing angles, low power consumptions, and customizable screen shapes.
The LED display screen is composed of a plurality of independent LED light-emitting units arranged in an array. FIG. 1 is a front wiring diagram of a light-emitting unit in a prior art, and FIG. 2 is a back wiring diagram of the light-emitting unit in FIG. 1. Referring to FIG. 1 and FIG. 2, each of light-emitting units includes an insulating substrate 20, four metal pads, one anode pin, three cathode pins, and LED chips having three colors of red, green, and blue. Three LED chips are respectively fixed on a first chip bonding pad 21, a second chip bonding pad 22, and a third chip bonding pad 23. Anodes of the three LED chips are connected to the common anode pad 24, and are connected to the anode pin P1 on the back of the insulating substrate 20 through metal vias. Cathodes of the three LED chips are connected to respective cathode pads, and are connected to respective cathode pins. In FIG. 1, the LED chips on the second chip bonding pad 22 and the third chip bonding pad 23 are vertical chips, and the cathode is fixed on the second chip bonding pad 22 and the third chip bonding pad 23 through conductive adhesive, wherein the second chip bonding pads 22 and the third chip bonding pad 23 both serve as the cathode pads of the two chips thereon, and a portion of the first bonding pad 21 serves as the cathode pad of the chip thereon, and the three cathode pads are respectively connected to the three cathode pins on the back of the insulating substrate through the metal vias. The three LED chips and the pads are covered by a transparent encapsulating material. When forming a display module, it is necessary to weld the pins of the plurality of independent LED light-emitting units onto a print circuit board (PCB). With the rapid development of LED display screen towards downsizing, the size of the corresponding light-emitting units also tends to be reduced. However, the conventional independent light-emitting unit has the problem that the welding operation is difficult and is easy to be sealing-off, and hence it is not favorable to transportation. Besides, the volume of the encapsulating material in the light-emitting unit is small, resulting in weak bonding force between the encapsulating material and the insulating substrate, poor sealing performance, and weak moisture resistance.